&#34;n&#34; output transmission line and transformer hybrid



Nov. 5, 1963 G. E. PET-rs nl', ETAL 3,109,998

"N" OUTPUT TRANSMISSION LINE AND TRANSFORMER HYBRID l Filed oct. 20 -1961 2 sheets-sheet 1 V TETE.'

gamut [UM .a2/1.3.4@ ATTO R N EY Nov. 5, 1963 G. E. PETTs nl, ETAL 3,109,998

"N" OUTPUT TRANSMISSION LINE AND TRANSFORMER HYBRID Filed Oct. 20, 1961 2 Sheets-Sheet 2 @LMAQMW ATTO R N EY United States Patent O IThis invention relates to line hybrids of the type which provide la number of outputs derived lfrom one input wherein these outputs are isolated from one another without 'any theoretical loss of power. More particularly, the inventionrelates to an N type (any number of outputs) of the transmission and transformer hydrid.

Devices of the yfor-nr Where a single input is to be fed into a number of systems or equipments require the u-se t of a circuit for dividing up this available input without lany interaction between the respective outputs. A simple example or one such system requiring input distribution is `an antenna system where in one case it is desired to connect the antenna to a number of receivers and in another to -apply the signal from a transmitter to a multiple antenna array. In the past, it has been necessary in order to provide more than two balanced isolated outputs to employ a cascaded hybrid arrangement. This in eiect requires the use of hybrids each of which have two outputs. These hybrids are connected in such a fashion that for each output another cascaded hybrid is placed thereaicross. In other words, the two outputs of the lirst hybrid are te-rminated by the inputs of two other hybrids and these in turn `are terminated `by the next 4succeeding four hybrid stage which has eight outputs. The progression is continued until the desired number of outputs are attained. Basically, it is obvious that by this cascaded method the .number of outputs obtainable with equal signal or input power division is an integral power of two (2n). If someone therefore is in need o-f Ian odd number of outputs or a 4number that is not -a multiple of 2n he must discard a certain number or outputs. Economically, this cascaded method is both unsound and unrealistic when one considers that not only must certain outputs be discarded but they must 'also be properly terminated in order to insure impedence matching and equal power distribution. Further, the number of unused outputs will increase with any large number of required outputs 'and the bulk, weight and overall size of the equipment will increase substantially while the :available power at any one output will decrease.

It might be assumed that this problem `can be solved by merely providing the required number of outputs but this is not la simple problem when one considers the other necessary features such as equal power distribution, impedance matching yand most important the high degree of electrical isolation between the outputs. 'Presently available hybrids do satisfy these requirements but due to their principle of operation they can only provide a single pair of outputs for each input and therefore they must be cascaded as previously described when outputs in excess of two vare desired.

An object of this invention is to provide a device having a signal input and any number of desired outputs which are Ibalanced and isolated from one another.

Another object is to provide a simple, practical, eicient inexpensive and dependable N output hybrid.

Still another object is to provide an N hybrid transmission and'transforrner system of balanced and isolated outputs.

Other objects 'and advantages will be apparent troni the following description of embodiments of the invention, and the novel features thereof will be particularly 3,109,998 Patented Nov. 5, 1963 pointed out hereinafter in connection with the appended claims.

FIG. la is a diagram of a typical transmission line distribution system.

FIG. lb is a diagram of the transmission system of FIG. la using the legend notation.

FIG. 2 is a diagram of -a transmission line distribution system embodying the principle of this invention.

FIG. 3 is another embodiment of the invention.

FIGS. 4 and 5 illustrate schematically a transformer hybrid made in accordance with this invention.

The circuit of FIG. la illustrates a typical network for the distribution of a signal to various outputs. For the sake of clarity only .three branches have Ibeen shown =a1 though any number N may be used. The circuit consists off N quarterwave transmission lines lil connected in parallel at one end to a common junction or terminal 11 |across which ya source 12 may be placed. Each transmission line l@ at its end opposite the source o r terminal 11 is terminated in a load impedance ZLIB. In order to properly match the source `12 to its input circuit which includes the transmission line lll whose characteristic impedance is Z0 and the load ZL the proper line `impedance is necessary. The impedance for each quarter-wave 'branch is yand if there are N branches in parallel then the total impedance is equal to should eliectively Ibe equal to the total branch impedance namely If the source impedance is equal to the load impedance this reduces to FIG. 1b and the accompanying legend show the circuit of FIG. la using the notations of the legend. Considering now the circuit of FIG. l it is quite obvious that the outputs are not isolated from each other as there are direct paths through the terminal 1l connecting these outputs together. It is to solve this problem that the two or dual isolated output hybrid was devised. On the other hand this solution did not alleviate the ldifficulties that arise when the number of required outputs is rgreater than two and not a multiple of 2, FIG. 2 illustrates an embodiment made in accordance with this invention as ap'- plied to a triple output and for clarity the notation of the legend of FIG. 1 has been employed. The source 22 is again connected to the output 23 by transmission line 20 which in ellect is the equivalent circuit of FIG. l. A direct path is now provided between each of the outputs, which path, comprises in each case a length of transmission line 24, a balance termination 25, a phase inverter 26 (180 phase shift) and `a second transmission line 2.7. The transmission lines are chosen so that their characteristic impedance maintains va matched condition between the outputs and the interposed components. The balance termination may be of the resistive rtype or a tuned net- Work while the phase inverter made by any suitable device as for example, a simple RC phase shift network or a coupled winding. With this arrangement, an injected signal will divide equally |between the paths (from one output to the source, then to a second output, and through the inverting path between the outputs, and with equal impedances the two signals arriving at an output will be It 180 out of phase due to the inventing path thus providing electrical isolation (cancellation) between each of the outputs.

In all cases irrespective of the number of outputs (N) a second inverted path must be introduced between every pair of outputs where isolation is desired. FIG. 3 illustrates this for a line hybrid having 'four separate isolated outputs and similar systems can be devised with any number of isolated outputs 'employing the principle of this invention. The following relationships are useful in deriving these networks wherein N is the number of outputs.

'(a) The characteristic impedance of the transmission line is Z=\/ZL when the source and load impedances are equal,

' f(b) The number of individual transmission line segments is (N-6),

(c) 'Ihe number of resistors in which no power is dissipated-is (2N-3),

(d) The total number of terminations and sources is (3N-2), and

(e) The number of transmission lines attached to the input or to any output is N. 1

In the illustrated embodiment of FIG. 4 a number of identical transformers 40 each also designated as Tj, Tj and Tn form a part of an N output transformer hybrid. Although only three such transformers have been shown any number may be used depending on the number of outputs required. That is, the number of outputs (N) is equal to the number of transformers (N). Each transformer 40 is provided with one secondary winding 41 and N primary windings of which one 42 is an input winding and the others 43 are balance windings. The turns ratio of the primary to the secondary winding is and the dot associated with each Winding indicates inefect the direction of the winding. The input windings 42 are connected in series with the dot end of one winding connected to the undotted end of the next succeeding winding. Across these series windings is the signal input which for later explanation is represented by a source resistance 44. A current is is represented as owing in this input path. One balance Winding 43 of each primary of each transformer is connected to a balance winding of another separate transformer so that every transformer is connected to another by a balance winding. The balance windings are reverse connected such that the dotted ends are joined and undotted ends also joined. A balancing element, as for example resistor 45, is interposed between the balance windings and the current iiowing in this balance loop is designated as i1, i2, in. In FIG. 4, the balancing elements or resistors 45 are connected between the start ends of the balance windings while the finish ends are directly connected.

The transformer hybrid must satisfy three conditions, namely, provide isolation between the outputs, apply equal power to each output and match the source to the output. A circuit analysis of FIG. 4 will clearly show that the first condition is fully satisfied while a similar analysis of FIG. 5 will show the satisfaction of the two remaining conditions. Since there may be as many identical transformers 40 as desired we need consider only one of these, such as, Tj. The current ij flowing in the secondary maybe expressed in terms of the primary currents as, i

d Where z'a is the balance current in any transformer. The current is in the input winding 42 in terms of the output voltages E and the source impedance is T he balance winding current ia flowing between transformer Tj and any other transformer can be expressed in terms of the output voltages and .the balance resistance rb Now combining Equations 1a, 1b and 1c we have:

Equation 4d shows that the output current ij of any transformer is dependent only on the voltage across the output and the balance or source impedance. Therefore, since the output of any other transformer does not enter into the expression each output is isolated or is effectively independent of every other output. i

FIG. 5 illustrates the same embodiment as FIG. 4 except it is restricted to a showing limited to -three transformers and that the source 50` is represented as a voltage Es and an impedance r, and a load resistance r is across each of ythe outputs. Analyzing this circuit starting with the input rloop path we have:

where Ea is the output voltage of any transformer. Solv- Considering now any transformer Tj the current in the balance circuit between Tj Aand Ta is The primary and secondary currents of Tj are related as follows:

and with N j-l N ZEa-:Z-Eai'Ei'iZEa 1 1 j+1 (10) simplifies to Equation 13 above indicates that the output voltage for any output is dependent only on the input source voltage Es and independent of any other output. The power available at the output across the load resist-r r is:

PPE-i2 7 and from (13) E E wn so that while the maximum power vaila'ble from the source is i mf@ (15) 4r therefore f E52 Pr 47' 1 Fmg-guy (16) |and since there are N outputs the total powerl delivered by the source to all the loads is :Pme Equation 17 clearly shows that since the total power available at the source is delivered to the output loads then the hybrid transformer properly matches the source tothe output. For the specific case of FIGURE 5, N is equal to three.

, Summarizing the N output transformer hybrid of FIGS. 4 and' 5 and the attendant equations it is obvious that the circuit arrangement divides the available energy or power at the source equally to each of the outputs and further that each of the outputs are isolated from every other output. 'These equations have been derived Without regard to the number of outputs or transformers and therefore apply with equal force to an arrangement having any selected or predetermined number o-f outputs. For every output there is required an additional transformer `and an additional balance winding on each transformer which in and of itself makes this circuit simple, practical and inexpensive when compared to the cascaded arrangement presently used.

In addition to the uses of the N output hybrid systems previously mentioned they have particular application in conjunction with power dividers, balanced amplitude and phase detectors. Further, the hybrid fof this invention can be used as la directional coupler yfor various equipment, `such Ias, pulse reilectometers, broadband sweepers and pulse repeaters. The hybrid method herein-described has been used as an antenna coupler wherein it allows the number of equal gain outputs to be adjusted to the gain available -from the driver amplifier and thereby alleviates the necessity that the gain of the ampliiier be adjusted to give 2n outputs as is necessary when the cascaded method of interconnection is employed. This feature is especially critical where high frequency distributed amplifiers are in the circuit since there is a limitation on the number of vacuum tubes that can be placed on the `grid line due to the vacuum tube grid loading effects.

Obviously many modiiications and variations of the present invention are possible in the light of the above teachings. It is therefore to be understood that within the scope of the appended claims the invention may be practiced otherwise than as specifically described.

yWe claim:

1. An N output transformer hybrid wherein the input signal may be equally ydistributed to any number exceeding two of isolated outputs comprising N number, three or more, of transformers each having one secondary winding and N primary windings one of said primary windings being an input winding and the remaining primary windings being balance windings, said secondary 'widing being the output Winding, an input path including in series therein input terminals and said input windings of said transformers, a number -of balance electrical paths each including in series therein one balance winding of one of said transformers and la balance winding of another of said transformers, said balance windings in said balance path being connected in opposition whereby when a signal is applied to said input terminals the output at said. output terminals will be balanced and said youtput terminal will be electrically isolated from one another.

2. The transformer hybrid according toclaim 1 wherein al1 of said secondary windings have an equal number of turns.

`3. The transformer hybrid according to claim 2 wherein the turns ratio of said primary to secondary windings is one over the square root of the number of transformers.

4. The transformer hybrid according to claim 3 further including in said balance path in series therewith balancing means.

5. The transformer hybrid according to claim 4 Wherein said balancing means is a resistor element. 1

6. The transformer hybrid according to claim 5 wherein the resistance of said element is equal to the impedance 0f a signal source which may `be connected across said input terminals.

References Cited in the le of this patent UNITED STATES PATENTS 2,461,091 Stephenson Febf 8, 1949 2,863,003 Ridlcr et al DCC. 2, 1958 2,947,952 Hughes Allg. 2, 1960 OTHER REFERENCES 

1. AN "N" OUTPUT TRANSFORMER HYBRID WHEREIN THE INPUT SIGNAL MAY BE EQUALLY DISTRIBUTED TO ANY NUMBER EXCEEDING TWO OF ISOLATED OUTPUTS COMPRISING "N" NUMBER, THREE OR MORE, OF TRANSFORMERS EACH HAVING ONE SECONDARY WINDING AND "N" PRIMARY WINDINGS ONE OF SAID PRIMARY WINDINGS BEING AN INPUT WINDING AND THE REMAINING PRIMARY WINDINGS BEING BALANCE WINDINGS, SAID SECONDARY WINDING BEING THE OUTPUT WINDING, AN INPUT PATH INCLUDING IN SERIES THEREIN INPUT TERMINALS AND SAID INPUT WINDINGS 